Neutrinoless Double Beta Decay and new Physics Manfred Lindner 8. Mai 2013 M. Lindner, MPIK . 1
Adding Neutrino Masses to the SM Simplest and suggestive possibility: add 3 right handed singlets (1 L ) n R n R n L n R g N x n _ _ c æ ö æ c ö 0 m è ( ) n n ç D ÷ ç L ÷ ç ÷ ç ÷ x Majorana L R n m M è ø è ø R / < f > = v D R L like quarks and charged +9 param. & new ingredients: 6x6 block mass matrix leptons è Dirac mass terms 1) Majorana mass = scales block diagonalization M R heavy è 3 light n ’s (including NMS mixing) 2) lepton number viol. è SM+ M. Lindner, MPIK . 2
Other Possibilities Add scalar triplets (3 L ) or add fermionic (1 L ) or (3 L ) n L n L n L n L è left-handed Majorana 1,3 3 x x mass term: M L LL c x x _ Both n R and new singlets / triplets: m n =M L - m D M R -1 m D T è see-saw type II, III Higher dimensional operators: d=5, … _ è M L LL c M. Lindner, MPIK . 3
Radiative neutrino mass generation Add: more neutrinos, SUSY, extra dimensions, … è huge number of papers on neutrino masses... ... but we know only two D m 2 ... (plus mass & unitarity bounds) è neutrino masses can/may solve two of the SM problems: - leptogenesis as explanation of BAU (both Majorana and Dirac) - keV sterile neutrinos as excellent warm dark matter candidate even for n R only è BSM physics in many cases connections to LFV, LHC, DM M. Lindner, MPIK . 4
Double Beta Decay If neutrinos have Majorana masses è Lepton Number Violation è Neutrinoless Double Beta Decay BUT: Be careful about the inverted reasoning! M. Lindner, MPIK . 5
Double b -Decay & Mass Parabolas S Q Special nuclei: odd-odd even-even • single b decay energetically forbidden 76 Zn 76 Rb • double b decay allowed è GG-nuclei: 76 Ge, … b + b - 76 Ga 76 Kr 76 Br EC b - 76 As 76 Ge b - b + Q bb bb = 2039 keV 76 Se 30 31 32 33 34 35 36 37 Z 76 Ge: Only double b decay è SM: 2 n + 2e - *OR* BSM: 0 n + 2e - Further 0 nb nbb isotopes… In addition: isotopic composition, backgrounds, costs, NMEs, ... M. Lindner, MPIK . 6
The Standard Picture of Double Beta Decay 2 nb nbb 2 nbb decay seen for diff. isotopes (Kirsten,…) T 1/2 = O(10 18 - 10 21 years) è up to 10 11 ⊗ T Universe SM 0 nb nbb decay 0 nb nbb 2 nb nbb decay M ajorana mass T 1/2 > O(10 25 y) • observe 2 nb nbb 1/ t = G(Q,Z) |M nucl | 2 <m ee > 2 1/ • look for 0 nb nbb signal at Q bb bb è big amount of 0 nb nbb nuclei • extreme low backgrounds! è signal = Majorana mass important: NMEs and their uncertainties… M. Lindner, MPIK . 7
m ee : The Effective Neutrino Mass Comments: • cosmology: m < 0.2-0.3 eV • 0 nbb nbb : m ee < 0.1-0.3 eV • NMEs è unavoidable theory errors • known D m 2 from oscillations è yellow/blue areas è improved sensitivity is very promising! • warnings: - assumes no *other* D L=2 physics - assumes no sterile neutrinos, ... M. Lindner, MPIK . 8
More general: L Violating Processes 2 nb nbb exp. search unchanged… 0 nb nbb decay SM 2 nb nbb decay 0 nb nbb …interpretation changes: BSM T 1/2 > 0 nb nbb O(10 25 y) some D L=2 operator M. Lindner, MPIK . 9
Other Double Beta Decay Processes Standard Model: + è 2 electrons + 2 neutrinos 2 nb nbb Majorana n -masses or other D L=2 physics: è 2 electrons 0 nb nbb … SM+Higgs triplet SUSY SM + Higgs triplet SUSY Majorana neutrino masses important connections to LHC and LFV … ßà ßà Dirac? ßà TeV scale physics sub eV Majorana mass ßà M. Lindner, MPIK . 10
Interference of D L=2 Operators Usually with interferences = overall phase space factor ßà determined by parameters of new physics m e ~ ( L new ) -5 m 0 nb çè L new ~ TeV nbb = 1 eV çè M. Lindner, MPIK . 11
Extreme Cases m e m e from other D L=2 physics m ee from Majorana neutrinos only and no other D L=2 physics with Dirac neutrino masses and anything in-between M. Lindner, MPIK . 12
m e m’ ee interferences growing m e for fixed 0 nb nbb à shifts of masses, mixings and CP phases à destroys ability to extract Majorana phases à sensitivity to TeV M. Lindner, MPIK . 13
Does 0 nb nbb Decay imply Majorana Masses? • Schechter-Valle Theorem è is misleading Any D L=2 operator which mediates the decay induces via loops Majorana mass terms è unavoidable: Majorana neutrinos…!? 0 nb nbb è some D L=2 operator Dürr, ML, Merle 4 loops è enforce d m n = 10 -25 eV è very tiny (academic interest) è cannot explain observed n masses and splitting's Extreme possibility: - 0 nb nbb = L violation = other BSM physics - neutrino masses = Dirac (plus very tiny Majorana corrections) + Dirac leptogenesis, + ... M. Lindner, MPIK . 14
The experimental Task 0 nb nbb decay 2 nb nbb decay • finite energy resolution è background from the tail of 2 nb nbb • extreme low background è does not mean no background è lines… è need a method to ensure that it is 0 nb nbb and not some background 1) two different isotopes 2) isotopic fingerprint M. Lindner, MPIK . 15
Sensitivity & Background (for a Majorana Mass) without background 1000 N A = Avogadro’s number W = atomic weight of isotope e = signal detection efficiency M = isotope mass t = data taking time è with background N’ = N + N background 100 è c = cts/keV/kg/yr ; D E = ROI ton-scale à M. Lindner, MPIK . 16
Which Isotope? - Large detector mass ßà natural abundance or enrichment (cost, time) ßà detection technology ßà ßà costs, feasibility, … ßà - Radio-purity ßà ultra clean 0 nbb source and instrumentation ßà high Q bb ßà ßà less bgd. - Good energy resolution bb + D E ßà avoid known and unknown backgrounds in ROI: Q bb ßà - Uncertainties in nuclear matrix elements + energy resolution è Germanium is a very good choice è use two different isotopes to confirm a signal … M. Lindner, MPIK . 17
Consistency Test with one Isotope ratio is set by nuclear spectra - independent of backgrounds! Duerr, ML, Zuber M. Lindner, MPIK . 18
The Fight against Background Extreme rare reaction (T>10 25 years >> age of Universe) Magnitude 1 decay/kg/year Environment ~ 30Bq/kg = 10 9 /kg/year è 3000/person/second è avoid single b decay ßà ßà suitable isotopes è avoiding / suppression of environmental radioactivity - in the 0 nb nbb detector material à ultra clean (production, handling) à puls form analysis (identify & reject background) - in the detector parts (e.g. holders, signal amplifiers) à lowest amount of material çè µ Bq/kg ) à ultra pure materials (selection; environmnt = O(100Bq/kg) çè à extremely helpful: 76 Ge source = detector (a big Ge diode) - in the environment à ultra clean room (clean room, …) à avoid Radon (decay of U, Th in the environment à 222 Rn-gas) à avoid cosmogenic activation (new isotopes à go underground) à avoid cosmogenic myons, neutrons à go underground M. Lindner, MPIK . 19
Experimental Realizations 0 nb nbb decay is important! è low background expertise! è long history and diverse plans for the future Important mile stone: Heidelberg-Moskau-Experiment (H.V. Klador-Kleingrothaus MPIK) EXO - for many years best limts nEXO - signal? è GERDA è important result KamLAND-Zen M. Lindner, MPIK . 20
The GERDA Collaboration http://www.mpi-hd.mpg.de/gerda/ INR Moscow ITEP Moscow Kurchatov Institute European Commission Joint Research Centre JRC Geel 16 institutions ~110 members 21 M. Lindner, MPIK . 21
Protection against Cosmogenic Radiation Unterground laboratory è Gran Sasso (Italy) 1400 m rock as shield (3100 mwe) GERDA A very special place to work… M. Lindner, MPIK . 22
The GERDA Detector (original idea by G. Heusser, MPIK) plastic scintillator veto clean room background reduction: lock system • material selection screening ( g , Rn, …) • • graded shielding water tank: 590 m 3 high purity water - deep underground neutron moderator/absorber - veto systems muon Cherenkov veto - water - operation in LiAr cryostat with - naked Ge internal Cu shield - … • source = detector very clean liquid Ar • puls shape analysis • … naked Ge detectors: 3 strings with 9 coax detectors 1 string with 5 BEGe’s scale model by A. Lindner M. Lindner, MPIK . 23
MPIK Material g -Screening Facilities • Different screening stations@MPIK underground lab: BRUNO, CORRADO, … (1mBq/kg) • 4 GEMPIs @LNGS (10 µ Bq/kg) • New: GIOVE @MPIK (50 µ Bq/kg) è extensive task for GERDA and other experiments (XENON, …) M. Lindner, MPIK . 24
Rn Screening Facilities Gas counting systems @LNGS and @MPIK 222 Rn emanation technique - sensitivity = few atoms/probe - large samples ßà ßà absolute sensitivity - non-trivial; not commonly available; routine @MPIK - established numbers: Nylon (Borexino) < 1 µ Bq/m 2 Copper (Gerda): 2 µ Bq/m 2 Stainless steel (Borexino): 5 µ Bq/m 2 Titanium: (100 + 30) µ Bq/m 2 New: Auto-Ema - automatized Rn screening facility @MPIK è many samples M. Lindner, MPIK . 25
BEGe Detector production ç accumulated activity and its decay beware of long-lived isotopes…! M. Lindner, MPIK . 26
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